1. Field of the Invention
The present invention relates to a gas laser tube, and more specifically to a structure of an anode which is located within an elongated envelope defining a gas filled space and which is in contact with the inner wall surface of the envelope at least when the laser is in an operating condition.
2. Description of Related Art
Gas lasers are composed of an insulative envelope filling therein a gaseous active medium such as argon and krypton. For example, with electric discharge in the envelope, the gaseous atoms are activated from a basic state to excited states so that a so-called laser oscillation is caused.
In order to cause transition from the basic state to the excited state, a very large energy is required. For example, in a so-called ion laser, it is necessary to supply a large electric current at the degree of several ten amperes so as to generate a suffcient discharge in the laser tube.
However, oscillation efficiency of the gas laser is very low. Namely, most of applied electric energy is converted to heat which is then exhausted in the form of heat to the external. Therefore, the gas laser will generate a very large mount of heat. For example, the amount of heat generated in the ion laser will reach several kilowatts to several ten kilowatts.
The large amount of heat will cause a deformation of a laser tube including in the insulative envelope, so that an optical quality of the generated laser beam is greatly deteriorated. In addition, if the deformation of the laser tube becomes remarkable, the laser tube itself will often be broken.
In the prior art, therefore, it has been an ordinary practice to provide a cooling mechanism to the laser tube in accordance with a heat resistance of the laser tube itself.
In such gas lasers provided with the cooling mechanism, the envelope and a laser capillary or discharge path member have been formed of ceramic materials having good heat resistance and high heat conductivity. Further, a cooling water is supplied to the outer surface of the ceramic envelope so as to sufficiently forcedly cool a portion of the envelope where an anode is located and which generates a large heat.
However, the conventional gas laser has another disadvantage caused by the force cooling. In the gas laser tube, an anode disc member is located within the tubular ceramic envelope in contact with the inner surface of the envelope. On the other hand, the anode is ordinarily made of metal having a coefficient of thermal expansion higher than that of the ceramic envelope.
Therefore, even if the laser envelope is in a forcedly cooled condition, since the temperature of the anode itself will be increased by operation of the laser, a stress will generate to act on the envelope in outwardly radial directions apply pressure radially against the envelope. The higher the temperature is, the larger this force becomes, Accordingly, if the temperature elevates too high, the ceramic envelope would be broken by the force caused by the thermal expansion